Weight loss maintenance (WLM) is the major challenge in weight management. While most individuals who lose weight intend to keep their weight off, decay in adherence to behavioral recommendations is common, leading to weight regain. Behavioral WLM interventions can help sustain healthy lifestyles but response to treatment is variable. Moreover, the mechanisms of action by which interventions exert their effects are not clearly elucidated, which has thwarted the development of more efficacious treatment approaches. To advance the science of behavior change, research is needed to identify putative targets that are engaged by WLM interventions and that drive behavior change. Temporal Self-Regulation Theory (TST) posits that whether intentions lead to behavior depends, in large part, on self-regulatory capacity (i.e., executive function). Particularly relevant to WLM is the cognitive construct of delayed discounting (DD), or the tendency to discount a larger future reward (weight management) in favor of smaller immediate rewards (e.g., a pleasurable sedentary activity). Experimental and clinical research suggests that DD is instrumental in behavioral decision- making and predictive of health behavior change but has yet to be explored in the context of WLM. Further, TST posits a moderating role for the environment such that when the costs of engaging in a behavior (e.g., exercising in bad weather) are more proximal than its benefits (health improvements), self-regulatory constructs such as DD will be a stronger determinant of behavior. The aim of the proposed study is to test whether, as predicted by TST, delayed discounting mediates adherence to physical activity (PA) recommendations in WLM interventions and whether environmental factors moderate this relationship. PA is the behavior of focus as it is a robust predictor of WLM success and can be measured objectively in the natural environment. This work is novel because it will use an experimental medicine approach to establish whether DD is engaged by a behavioral WLM intervention that explicitly targets DD through the use of episodic future thinking, a visualization procedure that shows promise in amplifying the value of long-term rewards, thus reducing DD. Temporal associations between engagement of DD and physical activity will be examined with real time data capture methods (Ecological Momentary Assessment and accelerometry) providing a nuanced understanding of how/when the putative target (DD) is in engaged in WLM treatment and whether this engagement predicts sustained PA behavior change. This intensive within-person longitudinal design will also allow for an exploration of how environmental factors moderate the delayed discounting-physical activity link, setting the stage for a future just-in-time adaptive intervention for weight loss maintenance.